The vertical
tail consists of a structural fin surface, the rudder/speed brake
surface, a tip and a lower trailing edge. The rudder splits into
two halves to serve as a speed brake.

The vertical
tail structure fin is made of aluminum. The main torque box is constructed
of integral-machined skins and strings, ribs, and two machined spars.
The fin is attached by two tension tie bolts at the root of the
front spar of the vertical tail to the forward bulkhead of the aft
fuselage and by eight shear bolts at the root of the vertical tail
rear spar to the upper structural surface of the aft fuselage.

The rudder/speed
brake control surface is made of conventional aluminum ribs and
spars with aluminum honeycomb skin panels and is attached through
rotating hinge parts to the vertical tail fin.

The lower trailing
edge area of the fin, which houses the rudder/speed brake power
drive unit, is made of aluminum honeycomb skin.

The hydraulic
power drive unit/mechanical rotary actuation system drives left-
and right-hand drive shafts in the same direction for rudder control
of plus or minus 27º. For speed brake control, the drive
shafts turn in opposite directions for a maximum of 49.3º
each. The rotary drive actions are also combined for joint rudder/speed
brake control. The hydraulic power drive unit is controlled by the
orbiter flight control system.

The vertical
tail structure is designed for a 163-decibel acoustic environment
with a maximum temperature of 350º F.

All-Inconel
honeycomb conical seals house the rotary actuators and provide a
pressure and thermal seal that withstands a maximum of 1,200º F.

The split halves
of the rudder panels and trailing edge contain a thermal barrier
seal.

The vertical
tail and rudder/speed brake are covered with a reusable thermal
protection system. A thermal barrier is also employed at the interface
of the vertical stabilizer and aft fuselage.

The contractor
for the vertical tail and rudder/speed brake is Fairchild Republic,
Farmingdale, N.Y.